Abstract Nearly 65% of adults in the United States actively try to increase their protein intake by consuming naturally protein-rich foods and foods and drinks fortified with protein isolates to improve their health. However, data from recent population studies have shown high protein consumption is associated with an increased risk of developing type 2 diabetes (T2D). This adverse effect might be specific to the type of protein consumed because several studies have found high animal protein, but not high plant protein, consumption was associated with increased T2D risk. There is experimental evidence from studies conducted in people and in mice to support a causal relationship between dietary protein intake and metabolic dysfunction. However, the effect of chronic high protein intake on glucose homeostasis and the mechanisms that cause protein-mediated metabolic dysfunction are not known. The reason(s) for the differences in the metabolic effects observed between high animal protein and high plant protein consumption are also not known, but could be due to differences in the amino acid composition and structure of animal and plant proteins per se and/or their biological matrix, which includes complex cell walls, lectins, and protease inhibitors in protein-rich plant foods, that can impair gut microbial access to proteins and/or induce the microbial production of beneficial metabolites, such as short-chain fatty acids. The goal of this proposal is to determine the effect of a high- protein diet in which the increase in protein intake is derived from different sources (animal vs plant and protein-rich whole foods vs protein isolates) on: i) liver and muscle insulin sensitivity; ii) the metabolic response to a meal, and iii) 24-h plasma concentration profiles of glucose, glucoregulatory hormones, and protein-derived metabolites purported to cause metabolic dysfunction. Our overarching hypothesis is that diets enriched with either animal or plant protein isolates, or animal protein-rich whole foods, but not plant protein-rich whole foods, cause alterations in the plasma hormones and protein metabolites that can cause insulin resistance and stimulate hepatic glucose production, thereby raising 24-h plasma glucose concentration.